name of a legendary swift horse
騄 is a rare kanji that names a specific legendary swift horse. Its meaning is limited to that proper-name sense and does not extend to general horse or speed vocabulary.
騄 combines 馬 (horse) with 录, which likely contributes the sound. The character was created to name a specific legendary horse, so its origin is tied to that proper name rather than a general descriptive meaning.
The left side 馬 is a horse, and the right side 录 looks like a record or log. Imagine a legendary horse so fast its name is recorded in the logs: 騄 is that swift horse.
For リョク, picture the legendary horse galloping with a rhythmic lock-step beat: lock -> リョク, and the horse's name echoes that swift sound.